1. Field of the Invention
The present invention relates to multi-domain system in-plane switching type liquid crystal display device.
2. Description of the Related Art
Conventionally, multi-domain systems have been developed for in-plane switching type liquid crystal display devices (for example, refer to Japanese Patent Laid-Open Publication No. 2002-323706, FIG. 15 and FIG. 47 as well as Japanese Patent Laid-Open Publication No. 2002-258321, FIG. 8). A multi-domain system is a system in which pixel electrodes and common electrodes, formed on an active element substrate, are formed in a zigzag shape to form one pair of sub-pixel regions (domain) on each unit pixel. In other words, a first portion, extending in a direction sloping towards the rubbing direction of an oriented film, and a second portion, extending in a direction sloping on the opposite side of the first portion towards that rubbing direction, are alternately arranged on each pixel electrode and each common electrode. Consequently, the directions of the electric fields applied to the liquid crystal molecules are different from each other in each unit pixel and because of this, two sub-pixel regions are formed wherein the rotation direction of the directors of the liquid crystal molecules are opposite to each other. As a result, because these two sub-pixel regions optically compensate each other, coloring that is seen when viewing a liquid crystal display device from an oblique direction as well as tone reversal that occurs between a black display and a half-tone display are controlled, making it possible to obtain even better viewing angle characteristics.
FIG. 1 is a partially enlarged plan view showing a conventional multi-domain system in-plane switching type liquid crystal display device. FIG. 2 is a cross-sectional view taken along the line C-C′ shown in FIG. 1. FIG. 3 is a cross-sectional view taken along the line D-D′ shown in FIG. 1. As shown in FIG. 1 to FIG. 3, an active element substrate 2 and an opposing substrate 103 are provided in this conventional liquid crystal display device 101 parallel to each other. A liquid crystal layer 4 is formed between the active element substrate 2 and the opposing substrate 103. This liquid crystal display device 101 is a normally black type liquid crystal display device.
A glass substrate 5 is provided on the active element substrate 2 and a gate insulation film 6 is provided on the upper surface of the side opposite the opposing substrate 103 on the glass substrate 5. A passivation film 7 is provided on the gate insulation film 6. In addition, a data wiring 8 is provided in one region on the passivation film 7. The data wiring 8 is formed in a zigzag pattern viewed from a direction perpendicular to the surface of the glass substrate 5 (hereinafter referred to as “viewed as a plan view”). In other words, a portion 8a, extending in a direction that slopes and forms a fixed angle with respect to a rubbing direction 31 (described later), and a portion 8b, extending in a direction that slopes to the side opposite to the direction in which the portion 8a extends with respect to the rubbing direction 31 and forms an angle with the same size, are alternately arranged.
A convex shaped insulation film 9 is provided on the passivation film 7 so as to cover the data wiring 8. The insulation film 9 is formed in a zigzag pattern in like manner to the data wiring 8 when viewed as a plan view. As shown in FIG. 2 and FIG. 3, the side of the convex shaped insulation film 9 is sloped. Furthermore, a common electrode 10, composed of a transparent conductive material, is provided so as to cover the upper surface and side surface of the insulation film 9. Because of this, the common electrode 10 can shield the data wiring 8. When viewed as a plan view, the common electrode 10 is formed in a zigzag pattern in like manner to the data wiring 8 and the insulation film 9 and the region where the common electrode 10 is formed is wider than the region where the insulation film 9 is formed. Consequently, the insulation film 9 is completely covered with the common electrode 10 and one part of the common electrode 10 is also formed in the region 32 except for the region directly above the insulation film 9. Even further, an oriented film 11 is provided over the passivation film 7 and the common electrode 10 on the entire surface of the glass substrate 5. The surface of the oriented film 11 is rubbed along the rubbing direction 31 shown in FIG. 1. The gate insulation film 6, the passivation film 7, and the oriented film 11 are not shown in FIG. 1.
In contrast, a glass substrate 21 is provided on the opposing substrate 103 and a shielding layer 26 is locally provided on the upper surface of the side opposite the active element substrate 2 on the glass substrate 21. When viewed as a plan view, the shape of the shielding layer 26 is a straight line. When viewed as a plan view, the shielding layer 26 is formed such that it does not protrude from the region directly above the common electrode 10 of the active element substrate 2 to prevent reductions in the numerical aperture of the pixels.
A colored layer 23 is provided on both sides of the shielding layer 26 on the glass substrate 21 and the edge of the colored layer 23 rests on the edge of the shielding layer 26. In addition, an overcoat layer 24 is formed so as to cover the shielding layer 26 and the colored layer 23. An oriented film 25 is also provided on the overcoat layer 24. The surface of the oriented film 25 is rubbed along a fixed direction.
The following problems existed in the conventional technology described above. As shown in FIG. 2 and FIG. 3, the shape of the insulation film 9 is a convex shape and protrudes from the periphery. Because of this, the sloping area of the insulation film 9 does not have sufficient rubbing in the rubbing process of the oriented film 11 while manufacturing a liquid crystal display device. In particular, it is easier for the rubbing of the falling sloping area to be less adequate than the rising sloping area. Consequently, it is much easier for the rubbing in the region 33 shown in FIG. 1 to be inadequate. Therefore, it is difficult to control the orientation of the liquid crystal material in the region 33.
When an electric field is not applied to the liquid crystal layer in a normally-black liquid crystal display device, the liquid crystal material is oriented by the action of the oriented film only to achieve a black display. Because of this, the orientation state of the liquid crystal material has a great influence on the transmittance in the liquid crystal layer 4 while displaying a black display and if the orientation is disturbed, the transmittance will increase. Thus, because the rubbing implemented on the oriented film 11 is poor in the region 33 and the action that orients the liquid crystal material is poor, the transmittance in the region 33 of the liquid crystal layer 4 inevitably becomes higher.
As shown in FIG. 1, the shielding layer 26 is formed in a straight line such that it does not protrude from the region directly above the common electrode 10 in order to prevent reductions in the numerical aperture of the liquid crystal display device. In contrast, when viewed as a plan view, the shape of the convex-shaped insulation film 9 is a zigzag shape. Because of this, an area where the shielding layer 26 is not provided develops in the region directly above the insulation film 9. The region 33 is also included in this type of area. Therefore, light transmitted through the liquid crystal layer 4 in the region 33 while displaying a black display is not blocked by the shielding layer 26 and ends up leaking outside the liquid crystal display device. In addition, the brightness while displaying a black display, or namely the black brightness, becomes higher as well. In contrast, if the width of the shielding layer 26 is made wider, the light leakage can be reduced although the numerical aperture will be reduced. If the black brightness is increased or if the numerical aperture is reduced, the contrast of the image display will be reduced.
Moreover, if the rubbing strength is unreasonably increased in order to improve the orientation force of the oriented film 11, the oriented film 11 will not be able to bear the rubbing and detach. The resulting image quality will be reduced due to that detached mark and detached refuse.